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Discontinuation of Primidone Testing

September 1 2022
Effective Oct 1, 2022, we will discontinue Primidone Testing.

Effective Oct 1, 2022, we will discontinue Primidone Testing. Any Primidone order will be substituted with a phenobarbital measurement and reported with the following comment: “Phenobarbital is the major active metabolite of Primidone.”

Primidone tends to be unbound to serum proteins and demonstrates significant inter-dosage variability in measured concentration.1 A product of the hepatic metabolism of primidone is phenobarbital, which is believed to be the predominant active metabolite.2 Phenobarbital tends to be higher than primidone when the concentration is at a steady state and demonstrates lower inter-dosage variability in measured concentration.1 This makes it a better target for therapeutic drug monitoring.

For any clinical or technical questions regarding this change please contact the following LifeLabs biochemists:

Uvaraj Uddayasankar, PhD FCACB

Clinical Biochemist                      

T   416-675-4530 Ext. 42211

E uvaraj.uddayasankar@LifeLabs.com

 

Kika Veljkovic (she/her) PhD FCACB

Discipline Head, High Volume Chemistry

T   416-675-4530 Ext. 42832

Kika.Veljkovic@LifeLabs.com

Thank you,

Dr. Catherine Ross, MD, MSc, FRCPC

Medical Director, ON

T   647-943-2413 Ext: 42980

E catherine.ross@lifelabs.com

 

References:

  • Eadie, M. J. (1991). Formation of active metabolites of anticonvulsant drugs. Clinical pharmacokinetics21(1), 27-41.
  • Johannessen, S. I., & Johannessen Landmark, C. (2020). Anti-Convulsant Agents: Phenobarbital and Primidone. NeuroPsychopharmacotherapy, 1-10.

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